Deputy Prime Minister Nick Clegg has told ITV News his Conservative colleagues in the Coalition are "turning a blind eye" to the super rich being taxed on their lavish properties in the same way as those living in modest homes.
Chancellor George Osborne told ITV's The Agenda he rejects the idea of a "mansion tax", proposed by the Liberal Democrats and now backed by Labour, as it is a "tax con".
But Mr Clegg has told ITV News' Political Correspondent Libby Wiener that the current Conservative policy is "unfair".
The Conservatives need to speak for themselves.
I for the life of me don't understand why the Conservatives think it's ok that an oligarch can buy a palace in Regent's Park for tens of millions of pounds and pay the same council tax as a three-bedroom family house in Lewisham.
That is just unfair.
We can't keep turning a blind eye to the super wealthy basically being taxed the same way on their properties as hard working families across the country.
The Liberal Democrats have always been unambiguous that they want to make the tax system fairer.
The Conservatives don't want to do that.
They don't want, perhaps, to offend people in very large mansions.
They need to answer for themselves.
I'm absolutely sure that what we stand for is the right thing.
See the interview with Mr Clegg on ITV News At Ten, followed by Mr Osborne's appearance on ITV's The Agenda with Tom Bradby at 10.35pm.
More top news
The Duke and Duchess of Cambridge met young people who have battled mental health issues on Saturday.
Former Chancellor Lord Geoffrey Howe was Margaret Thatcher's longest-serving Cabinet minister, also taking on the role of Foreign Secretary.
Lord Geoffrey Howe is known by many for his resignation speech which was seen as the catalyst which destroyed Margaret Thatcher.